Disk drives are commonly employed in workstations, personal computers, portables and other computer systems to store large amounts of data in a readily-available form. Typically, the primary components of a disk drive are a head disk assembly and a printed circuit board assembly which when fixed to one another form a functional unit that is then connected to a computer, such as by insertion into a bay of a host computer.
The head disk assembly includes a base and a cover which collectively house a head stack assembly and a data storage disk mounted on a spindle motor assembly for rotating said storage disk, and an actuator arrangement, driven by a voice coil motor, for advancing a read/write head. A flex circuit transmits data signals to and from the read/write head of the actuator.
The operation of a hard disk drive necessarily generates noise such as airborne and structure borne noises. For example, the electromagnetic spindle and the electromechanical voice coil motors drive the device with the spindle motor continually rotating the storage disk(s), and the voice coil motor selectively driving the actuator(s) to position the read/write heads. The motors transmit resonances throughout the disk drive, creating structural vibrations and acoustical, audible noise of varying frequencies. Such noise is transmitted to other part of the disk drive such as the housing, the cover and the substantially-planar printed circuit board, which in turn, can amplify resonant frequency sound intensity, in effect acting as a speaker diaphragm.
The presence of acoustic noise in an operating disk drive is undesirable. Customers perceive loudness as an indication of lower quality. As such, acoustic characteristics may serve as a benchmark of product quality. Furthermore, the ever-increasing operational speed of computers mandates reductions in the data access time from disk drives, resulting in increases in the speed of spindle motor which in turn intensifies the overall disk drive noise. In addition, acoustics standards, such as those of the internationally-recognized European International Standards Organization (“ISO”), are regularly lowered, forcing manufacturers to design disk drives characterized by reduced acoustic noise.
Currently, one form reducing the noise associated with the operation of a disk drive is by use of visco-damping materials. Typically, a layer of visco-damping material, such as a plastic damping material, is located in various regions of the disk drive, such as in the cover, to dampen the noise generated by the operation of the disk drive.
While widely used in the art, the visco-damping materials are not without shortcomings. The damping capability of a layer of visco-damping material composition is related to the thickness of the layer but in such way that while increasing the thickness improves the attenuation capabilities of the layer for the airborne noises, it is not optimized for structure-borne noises. Conversely, while decreasing the thickness improves the attenuation capabilities of the layer for structure-borne noises, it decreases the same for airborne noises. Thus in determining the thickness of a visco-damping material for damping the overall noise associated with the operation of a disk drive, a trade-off must be disadvantageously made between the damping of structure-borne noises and airborne noises, and therefore impairing the usage of a visco-damping material to its full potential for damping of either noise.
Accordingly, what is needed is a noise-damping material that allows for increasing the damping of both structure-borne noises and airborne.